The invention relates to a step for an escalator or an element for a moving sidewalk.
Numerous attempts have been made to provide a step for an escalator or an element for a moving sidewalk with a sufficient stiffness while providing only a minimal amount of material. Especially for wide steps or elements which presently can have a width of a meter or more, the rearward portion of the stepping surface is especially critical with respect to stability.
On the other hand, steps for escalators and elements for moving sidewalks are produced in considerable numbers so that even a minimal reduction of their weight and material expenditure reduces the expenses for material but also may result optionally in weight reduction of the movable parts of the escalator or the moving sidewalk which is desirable for various reasons.
While aluminum injection molded steps exhibit material problems in regard to tension cracks, plastic steps have the additional problem that the step or element must be dimensionally stable whereby a minimal heat expansion coefficient is essential in order to ensure reliable operation without the step or element grinding or jamming when surpassing the specified tolerances.
A further problem is the manufacture of plastic steps because due to the preferred manufacturing method, i.e., injection molding, a heat shrinkage must be taken into consideration which, for known steps despite the already existing values gained from experience and respective corrective attempts, still causes a 30% reject rate.
Accordingly, different attempts have been made to improve the known steps or elements with respect to maintaining the required dimensions while ensuring minimal material expenditure and comparatively minimal manufacturing expenditure. For example, the steps according to WO 92/22491 and WO 95/23758 have, at the rearward end of the stepping surface, a reinforcement profile that may be embodied differently.
Such reinforcement profiles for aluminum steps are known from DE-OS 27 17 666 whereby these known solutions result in a comparatively great material expenditure or with respect to dimensional precision for temperature fluctuations, are unsatisfactory.
A comparable solution is also known from DE-PS 41 34 626 which has been used for defining the preamble. This known construction which, in practice, has proven successful, employs fiberglass-reinforced thermoplastic material for the unitary embodiment of the escalator step. This solution, however, for comparatively wide escalator steps has occasionally high tolerance, fluctuations especially when the different heat expansion coefficients of the under structure of the escalator of the fiberglass reinforced plastic with respect to the specified temperature range of the escalator is taken into consideration.
It is also known to stabilize the rearward portion of the escalator steps such that the rearward axle extends from end to end below the stepping surface. This is disclosed in DE-OS 25 18 440 which also relates to the use of plastic material. With this solution, the required stiffening can be achieved. However, it must be ensured that the axle relative to the plastic material of the step or of the element cannot slide, and, furthermore, this construction is rather complicated and also very heavy when employing steel axles.
It is therefore an object of the invention to provide a step or element for an escalator or a moving sidewalk according to the preamble of claim 1 which, with respect to stability in relation to material use in comparison to the prior art is beneficial, but comparatively inexpensively producible and also provides advantages with respect to dimensional stability for an expanded temperature range and with respect to the weight of the step or the element.